1. Field of the Invention.
The present invention relates to an ultrasonic device, having a piezoelectric vibrator used as an electromechanical conversion means, for converting an electric signal applied to the piezoelectric vibrator to the acoustic vibration and then converting the acoustic vibration again to an electric signal which is delivered from the piezoelectric vibrator.
2. Description of the Prior Art.
Conventional signal converters include, for example, a transducer in a circuit for a switching power supply. Switching power supplies are employed extensively as power supplies for telegraphic instruments, electric computers and so on. Conventional switching power supplies transduce a power supply with direct current to an electric power with high frequency by using a high speed switching effect of a semiconductor, and next control and rectify the electric power to obtain a favorite direct current. In order to miniaturize switching power supplies, it is necessary for instance to promote a technique for driving at higher switching frequencies and to size all sorts of parts down. On the other hand, driving at higher switching frequencies bring damages on a semiconductor and an electromagnetic transformer. Therefore, it is difficult to miniaturize switching power supplies. The damages on the semiconductor and the electromagnetic transformer increase over 1 MHz of switching frequencies. Accordingly, it is difficult to more miniaturize switching power supplies. In order to minimize the damage on the semiconductor, it is necessary to improve a delay of a switching action generated in a switching circuit by way of the resonance and so forth. In order to minimize the damage of the electromagnetic transformer, it is necessary to improve the materials of the electromagnetic transformer. However, remarkable improvements of the materials of the electromagnetic transformer are difficult.
There are various attempts for using a piezoelectric transformer in a circuit of switching power supply, Conventional piezoelectric transformers include a polarization converting type transformer made from piezoelectric ceramics (a), a side effecting type transformer made from a single crystal of LiNbO.sub.3 (b) and a longitudinal vibrating type transformer made from laminated ceramics (c).
The piezoelectric transformer with type (a) uses two piezoelectric ceramics whose polarization axises are different from each other and electrodes whose arrangement are contrived, in order to increase the voltage ratio of the input side to the output side. The piezoelectric transformer with type (a) employed as a transformer for generating high voltage has a small-sized and incombustible structure showing a difficulty of a large amplitude action on account of an acoustic damage of the materials, electric and acoustic hysteresis phenomena of the materials and so on.
The piezoelectric transformer with type (b) having a simple structure with a small damage of the crystal has a small transmissible power on account of the influence of minute cracks in the side section of the crystal. Moreover, the piezoelectric transformers with type (b) show characteristic disagreements with each other.
The piezoelectric transformer with type (c) has a laminated structure, where the piled layers of the input side to the output side is different and therefore the capacitance ratio of the input side to the output side is different. When the piezoelectric transformer with type (c) is applied in a power supply circuit, it is difficult to control the voltage ratio in case that a load resistance is low. Moreover, the piezoelectric transformer with type (c) is easy to be broken by the large power. In addition, it is difficult for supporting a piezoelectric body. Further, it is necessary to reinforce the support in proportion to the increase of power. However, excessive reinforcement is easy to break the piezoelectric body.